Exploration for, location of, and extraction of subterranean fluids, including hydrocarbon fluids, typically involves drilling operations to create a well. Drilling operations, particularly drilling operations involving rotary drilling, often utilize drilling fluids, also called muds, for a variety of reasons including lubrication, removal of cuttings and other matter created during the drilling process, and to provide sufficient pressure to ensure that fluids located in subterranean reservoirs do not enter the borehole, or wellbore, and travel to the surface of the earth. Fluids located in subterranean reservoirs are under pressure from the overburden of the earth formation above them. Specialized equipment is used to provide control of all fluids used or encountered in the drilling of a well.
Conventionally, well pressure control equipment may include a blowout preventer (BOP) stack that sits atop of a wellhead. The BOP stack may include ram BOP(s) and an annular BOP. An annular preventer is a large valve used to control wellbore fluids. In this type of valve, the sealing element resembles a large rubber doughnut that is mechanically squeezed inward to seal on either pipe (drill collar, drillpipe, casing, or tubing) or the openhole. The ability to seal on a variety of pipe sizes is one advantage the annular preventer has over the ram blowout preventer. Most BOP stacks contain at least one annular preventer at the top of the BOP stack, and one or more ram-type preventers below.
Above the annular BOP is often a managed pressure drilling/underbalance drilling rotating control device (RCD)/rotating head. The RCD/rotating head is a pressure-control device used during drilling for the purpose of making a seal around the drillstring while the drillstring rotates. Essentially, the RCD/rotating head is a diverter with holding pressure capability. This device is intended to contain hydrocarbons or other wellbore fluids and prevent their release to the atmosphere by diverting flow through an outlet below the sealing element.